This application claims the priority benefit of Taiwan application serial no. 90106703, filed on Mar. 22, 2001.
1. Field of the Invention
The invention relates to a wafer-level packaging. More particularly, the invention relates to a wafer-level packaging suitable for use with a flip-chip connection.
2. Description of the Related Art
As electronic technology progresses, the miniaturization of electronic products is increasingly emphasized. This miniaturization results in a more complicated and denser structure of electronic products. In electronic industries, the packaging of electronic devices thus requires package structures that have small dimensions and high density. In this context, many types of packaging structures are developed, such as ball grid array (BGA) packages, chip-scale packages (CSP), flip-chip (F/C) structure packages, multi-chip module (MCM) packages, etc.
Among the above-mentioned types of packaging structures, the flip-chip structure packages advantageously allow for a packaging structure that has a small surface, high pin counts, a short signal path, a low induction and a control of noise signals. Thus, the flip-chip structure is increasingly used in packaging electronic devices.
In the traditional flip-chip structure, an underfill must be filled between the chip and the carrier or printed circuit substrate onto which the chip is connected. The underfill can share the thermal stress generated between the carrier and the chip due to different coefficients of thermal expansion of the carrier and the chip. As a result, the bumps that electrically connect the chip to the carrier can be prevented from fatigue resulting from the thermal cycle.
However, with a packaging structure that is increasingly denser, the pitch between the bumps formed on the chip is consequently reduced. In a flip-chip structure, effectively filling the underfill without voids thus becomes difficult and increases the manufacturing cost. Solutions that can overcome the above-described problems to allow for a reliable flip-chip structure are thus needed.
An aspect of the present invention is to provide a wafer-level packaging in which a patterned stress buffer layer is adequately formed over the wafer to substitute for a conventional underfill process, such that the packaging can be simply achieved with a reduced cost.
To attain the foregoing and other aspects, the present invention, according to a first preferred embodiment, provides a wafer-level packaging comprising: providing a wafer having a plurality of bonding pads thereon exposed through a passivation layer formed on the wafer, an under bump metal (UBM) being formed on each of the bonding pads; forming a stress buffer layer that can be patterned over the wafer, wherein using the pattern property of the stress buffer layer, a plurality of first openings are formed in the stress buffer layer exposing the under bump metals (UBM); filling a solder material in the first openings of the stress buffer layer; arranging either a stencil or a patterned photoresist having a plurality of second openings on the stress buffer layer such that the second openings expose the first openings; filling a solder material in the second openings; and performing a reflow process, wherein if the stencil is used, it is removed before the reflow process while if the patterned photoresist is used, it is removed after the reflow process.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.